Actually, it does in fact work.
Open the save in your hex editor.
Line 00001370. Values 9-12 are for Growth Points, 13-16 are for Gems. I have been able to get 9,999,999 Growth Points, haven't tested above 999,999 Gems though.
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The thing is, to enter the values backwards in the code.
9,999,999 is normally 5F5E0FF but you have to enter it as FF E0 F5 05. Likewise Gems would be F423F but you put it in as 3F 42 0F.
I have not tried to even look for the other values for stuff...